This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-124682, filed Apr. 23, 2001; and No. 2002-117602, filed Apr. 19, 2002, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an X-ray flat panel detector used in an X-ray diagnostic system.
2. Description of the Related Art
An X-ray flat panel detector is an X-ray detector used in an X-ray diagnostic system which displays as a halftone image the intensity of X-rays having passed through the body of an object to be examined. X-ray flat panel detectors are recently being put into practical use in place of I.I. (Image Intensifier) and an imaging plate which have conventionally been used. X-ray flat panel detectors can be classified into a direct conversion type and indirect conversion type depending on an incident X-ray conversion method. X-ray detection and read arrangements of the respective types are as follows.
In the direct conversion method, incident X-rays are converted into electron-hole pairs by a photoelectric conversion film. The converted electron-hole pairs are supplied as charges by an externally applied high electric field to pixel electrodes arrayed in a matrix. The electron-hole pairs are accumulated in the pixel electrodes. The accumulated charges are sequentially read out as electrical signals to an integrating amplifier via a signal line under the control of switching elements (TFTs) (scanning lines are driven from an OFF potential to an ON potential). The readout signals are A/D-converted into image data, which is output to a subsequent processing system.
In the indirect conversion method, incident X-rays are temporarily converted into light by a phosphor, and the light is converted into electron-hole pairs by a photoelectric conversion film. The generated charges are supplied by an externally applied high electric field to pixel electrodes arrayed in a matrix. The charges supplied to the pixel electrodes are processed similarly to the direct conversion method, generating image data.
In general, the X-ray flat panel detector has effective pixels for acquiring diagnostic image data, and a pixel group for removing noise components from signals detected by the effective pixels. Pixels which constitute the pixel group are called dummy pixels. The dummy pixels are used to remove noise components generated when the potential of a scanning line which forms a capacitance (parasitic capacitance) together with a signal line changes and charges which depend on the potential change flow into the signal line. Each dummy pixel is covered with a protective electrode for preventing dielectric breakdown caused by application of a high electric field.
The protective electrode formed on the dummy pixel forms a capacitance together with the signal line or scanning line connected to the dummy pixel. When the dummy pixel is driven, the potential of the protective electrode is distributed on the surface and becomes unstable. The unstable potential of the protective electrode is transferred to the signal line of the dummy pixel and superposed as a noise component on the signal line. The effective pixel area is not influenced by the unstable potential of the protective electrode. For this reason, the output values of the effective pixel and dummy pixel differ from each other in the absence of X-rays. This difference may act as an offset within the output range of an A/D converter.
The X-ray flat panel detector has a wiring line for static protection in a switching element array (TFT array) manufacturing process (antistatic wiring line will be called an xe2x80x9cLC wiring linexe2x80x9d hereinafter). The LC wiring line is not necessary in the use of the X-ray flat panel detector, but is generally left without removing it. However, the LC wiring line forms a conductive path: scanning line for driving the dummy pixelxe2x86x92the dummy pixelxe2x86x92LC wiring linexe2x86x92the effective pixelxe2x86x92scanning line for driving the effective pixel. When the dummy pixel is driven in actual X-ray detection, the fluctuation component of the scanning line potential of the dummy pixel is superposed on the potential of each scanning line of each effective pixel via this conductive path, increasing noise.
It is an object of the present invention to provide an X-ray flat panel detector capable of acquiring a low-noise, high-quality X-ray diagnostic image.
According to the first aspect of the present invention, there is provided an X-ray flat panel detector comprising an effective pixel array in which a plurality of pixel electrodes are arrayed in a matrix and accumulate charges, a photoconductor which covers the effective pixel array and generates charges on the basis of incident X-rays, a bias electrode which is formed on a second surface of the photoconductor, covers an area of the pixel electrodes, and applies a bias voltage between the photoconductor and the pixel electrodes, a plurality of signal lines to read out electronic signals from the effective pixel array, a plurality of scanning lines to scan the effective pixel array, first dummy pixels which are arranged adjacent to the effective pixel array and remove noise superposed on the plurality of signal lines, second dummy pixels which are arranged adjacent to the effective pixel array and remove noise superposed on the plurality of scanning lines, a first protective electrode which is arranged in correspondence with the first dummy pixels and electrically shields the bias electrode and the plurality of signal lines or the plurality of scanning lines, and a second protective electrode which is arranged in correspondence with the second dummy pixels, disconnected from the first protective electrode and electrically shields the bias electrode and the plurality of signal lines or the plurality of scanning lines.
According to the second aspect of the present invention, there is provided an X-ray flat panel detector comprising an effective pixel array in which a plurality of pixel electrodes are arrayed in a matrix and accumulate charges, a photoconductor which covers the effective pixel array and generates charges on the basis of incident X-rays, a bias electrode which is formed on a second surface of the photoconductor, covers an area of the pixel electrodes, and applies a bias voltage between the photoconductor and the pixel electrodes, a plurality of signal lines to read out electronic signals from the effective pixel array, a plurality of scanning lines to scan the effective pixel array, first dummy pixels which are arranged adjacent to the effective pixel array and remove noise superposed on the plurality of signal lines, second dummy pixels which are arranged adjacent to the effective pixel array and remove noise superposed on the plurality of scanning lines, and a protective electrode which is formed in such a way to deviate from a position facing to at least either the first dummy pixels or the second dummy pixels and electrically shields the bias electrode and the plurality of signal lines or the plurality of scanning lines.
According to the third aspect of the present invention, there is provided an X-ray flat panel detector comprising an effective pixel array in which a plurality of pixel electrodes are arrayed in a matrix and accumulate charges, a photoconductor which covers the effective pixel array and generates charges on the basis of incident X-rays, a plurality of first signal lines to read out electronic signals from the effective pixel array, a plurality of first scanning lines to scan the effective pixel array, and an electrostatic dispersion wiring line which is connected directly or via a nonlinear element to at least one of the plurality of first signal lines and at least one of the plurality of first scanning lines, and distributes static electricity accumulated in at least one of the plurality of first signal lines or the plurality of first scanning lines, wherein the electrostatic dispersion wiring line has a first auxiliary wiring line to disconnect the electrostatic dispersion wiring line between a connecting portion between the electrostatic dispersion wiring line and at least one of the plurality of first signal lines and a connecting portion between the electrostatic dispersion wiring line and at least one of the first scanning lines.
According to the fourth aspect of the present invention, there is provided an X-ray flat panel detector comprising an effective pixel array in which a plurality of pixel electrodes are arrayed in a matrix and accumulate charges, a photoconductor which covers the effective pixel array and generates charges on the basis of incident X-rays, a plurality of first signal lines to read out electronic signals from the effective pixel array, a plurality of first scanning lines to scan the effective pixel array, an electrostatic dispersion wiring line which is connected directly or via a nonlinear element to at least one of the plurality of first signal lines and at least one of the plurality of first scanning lines, and distributes static electricity accumulated in at least one of the plurality of first signal lines or the plurality of first scanning lines, first dummy pixels which remove noise superposed on the plurality of signal lines, second dummy pixels which remove noise superposed on the plurality of scanning lines, a plurality of second signal lines to read out electronic signals from the first dummy pixels, and second scanning lines to scan the second dummy pixels, wherein the electrostatic dispersion wiring line has a first wiring line which is connected to at least one of the plurality of first signal lines and at least one of the plurality of second signal lines, a second wiring line which is connected to at least one of the plurality of first scanning lines, and a third wiring line which is connected to at least one of the plurality of second scanning lines.